# Copyright (c) 2015 Sqreen. All Rights Reserved.
# Please refer to our terms for more information: https://www.sqreen.io/terms.html

begin
  Process.clock_gettime Process::CLOCK_MONOTONIC
  SQREEN_MONO_TIME = Process::CLOCK_MONOTONIC
rescue StandardError
  SQREEN_MONO_TIME = nil
end

module Sqreen
  # This module enable us to keep track of sqreen resource usage
  #
  # It is inspired by ActiveSupport::Notifications
  #
  module PerformanceNotifications
    @subscriptions_all = {}
    @subscription_id = 0
    class << self
      # Subsribe to receive notificiations about an event
      # returns a subscription indentitifcation
      def subscribe(&block)
        id = (@subscription_id += 1)
        @subscriptions_all[id] = block
        id
      end

      if SQREEN_MONO_TIME
        def time
          Process.clock_gettime(SQREEN_MONO_TIME)
        end
      else
        def time
          Time.now
        end
      end

      # Is there a subscriber
      def listen_for?
        !@subscriptions_all.empty?
      end

      # Instrument a call identified by key
      def instrument(key, meta = {}, &block)
        return yield unless listen_for?
        _instrument(key, meta, &block)
      end

      def notify(key, start, stop, meta = {})
        return unless listen_for?
        notifiers.each do |callable|
          callable.call(key, start, stop, meta)
        end
      end

      # Unsubscrube for a given subscription
      def unsubscribe(subscription)
        return unless @subscriptions_all.delete(subscription).nil?
      end

      # Unsubscribe from everything
      # not threadsafe
      def unsubscribe_all!
        @subscriptions_all.clear
      end

      private

      def notifiers
        @subscriptions_all.values
      end

      if SQREEN_MONO_TIME
        def _instrument(key, meta)
          start = Process.clock_gettime(SQREEN_MONO_TIME)
          yield
        ensure
          stop = Process.clock_gettime(SQREEN_MONO_TIME)
          notify(key, start, stop, meta)
        end
      else
        def _instrument(key, meta)
          start = Time.now
          yield
        ensure
          stop = Time.now
          notify(key, start, stop, meta)
        end
      end
    end
  end
end